1. Field of the Invention
This invention relates to protectors for the balloon of a balloon catheter.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for opening stenoses in the coronary arteries and in other parts of the vascular system. The most widely used form of angioplasty catheter includes an inflatable balloon at its distal end for dilation of the stenosis.
Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon clears the pathway through the artery.
One important characteristic of a dilatation balloon catheter used for angioplasty is its "profile", which is determined by the outer diameter of the distal end portion of the balloon, because a smaller diameter balloon (and catheter) can be more easily maneuvered through the coronary arteries and into the stenoses. Accordingly, considerable effort has been spent in developing low profile dilatation balloon catheters by minimizing the dimensions of the core or inner tube which extends through the balloon to its distal end, and by reducing wall thicknesses, to the extent possible, of the balloon itself.
Another important consideration is the outer diameter of the balloon in its deflated condition. In order to reduce the outer diameter of the balloon in its deflated condition, it is common to fold and/or wrap the flaps of the deflated balloon. When inflation fluid is applied to the deflated balloon, it causes the balloon flaps to unwrap so that the balloon can inflate to its full inflated state.
It has also been common to use a balloon protector in conjunction with a balloon dilatation catheter. The balloon protector wraps the balloon tightly in its deflated condition to minimize the outer diameter of the balloon in its deflated state. It also protects the balloon and the distal tip of the catheter from possible damage during shipping.
Some current balloon protectors are tubular units made of Teflon.TM., the inner diameter varying along the length of the tube so as to provide adequate compression at both the proximal and distal cones, the marker band area, and remaining areas of the balloon. These Teflon.TM. balloon protectors may be made by heat shrinking a Teflon.TM. tube down around a mandrel, resulting in a protector having some variability in size. A problem with such protectors is that in combination with the inherent variability in balloon size in any group of catheters, the variance in the balloon protectors may be large enough that all the balloon protectors will not fit any given catheter; the protector must instead be individually selected from the group to fit the catheter.
Another difficulty with current balloon protectors is that a protector which may originally hold the balloon tightly wrapped may become needlessly loose during final processing. The protector is typically placed around the balloon after the balloon is wrapped. The balloon is then heat set in its wrapped form and finally sterilized, all while the balloon protector is in place. The balloon shrinks during both processes, so that the protector may not hold the balloon wrap as tightly as might be desired, once the processes are complete.
In U.S. Pat. No. 5,053,007 to Euteneuer, a several-piece balloon protector is disclosed in which a compressible sleeve surrounding the balloon is compressed by two threaded, interlocking outer sleeves. Although the sleeve is disclosed to be of an elastic material, its inner diameter is slightly greater than the outer diameter of the balloon, and the large outer sleeves mechanically compress it.
In Hess, U.S. Pat. No. 5,066,298 a strip of non-elastic Teflon.TM. tape is wrapped helically around the balloon to compress it. The wrapping process, however, requires special machinery or time on the part of an operator to successfully wrap it.
Burns, et al., U.S. Pat. No. 5,137,512 discloses a multisegment balloon protector composed of two or more Teflon.TM. tubes, usually axially aligned and of different diameters, the advantage being that less force is required to apply the protectors, resulting in less damage to the fragile balloons.
Fuqua, in U.S. Pat. Nos. 4,738,666 and 4,710,181, discloses a longitudinally-folded catheter and a sheath which surrounds the catheter to hold it in a folded position. The catheter and sheath are inserted into the body, and the sheath removed so that the catheter unfolds and resumes its original, manufactured state. The sheath may be perforated to aid in removal. There is no indication that the sheath is smaller than, or forms an interference fit with, the catheter.
In Fuqua, the desired sheath is very thin (about 0.008 in.) and the sheath material has a high resilience and resistance to stretch measured by a "doxemeter rating of at least about 65%." Simply put, it appears that the desired sheath material is not elastic; rather it is largely inelastic, holding the catheter, which is compressible, in its folded shape. The intention is to compress the catheter, but not to permanently alter its configuration, since the catheter is intended to resume its original shape once the sheath is removed.
Cho, et al., U.S. Pat. No. 4,681,092, discloses a several-part wrapping apparatus for wrapping an intra-aortic balloon catheter. The device has channels to aid in wrapping the balloon and contains a shoe to bias the balloon in wrapped shape.
Hampson, U.S. Pat. No. 4,327,735, discloses a sleeve designed to protect the sterility of a catheter assembly, but does not hold a catheter balloon in wrapped condition. McFarlane, U.S. Pat. No. 4,573,981, discloses a sheath structure also designed to maintain catheter sterility, not to maintain a balloon in wrapped condition. Wolvek, et al., U.S. Pat. No. 4,444,186, discloses a wrapping guide which aids in spirally wrapping an intra-aortic balloon immediately before catheter use, but which does not hold the balloon tightly in a wrapped position.
This description of art is not intended to constitute an admission that any patent, publication, or other information referred to is "prior art" with respect to this invention unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C. F. R .sctn. 1.56 exists.